Intel: ADSP: move HPSRAM mask into assembly

Assembly in power_down() in power_down.S already defines data and
code to be locked in cache when powering down SRAM. Instead of adding
another such location in power.c, move the hpsram_mask[] array into
power_down.S.  This fixes hard to debug failures when shutting down
the ADSP.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>